1. Field of the Invention
The present invention relates to processes for making water-soluble β-hydroxynitriles. The present invention more particularly relates to processes for making β-hydroxynitriles from terminal 1,2-epoxides and inorganic cyanides.
2. Description of the Prior Art
β-hydroxynitriles may be prepared via ring-opening reactions between epoxides and cyanides or cyanide equivalents. Methanol is commonly employed as a solvent in ring-opening reactions of terminal epoxides because some cyanides, particularly potassium cyanide, are moderately soluble therein. A problem, however, with the use of methanol is the possibility of side reactions forming undesirable by-products. Upon reaction of the terminal epoxide and potassium cyanide, a potassium alkoxide of a β-hydroxynitrile is formed. The potassium alkoxide is highly alkaline and, along with residual cyanides, renders the reaction product mixture very alkaline. The potassium alkoxide may then react with methanol to form potassium methoxide, which may then react with the epoxide to form a methyl ether, an undesirable by-product.
One means employed in the prior art to address the problem of undesirable side reactions when using methanol as a solvent is to lower the alkalinity of the product mixture by implementing acidic reaction conditions. This, however, is problematic because acidic conditions may result in runaway or accelerated ring-opening reaction rates as well as in industrial hygiene and safety issues.
Another problem encountered is isolating water-soluble β-hydroxynitriles from reaction product mixtures. Isolation of non-water-soluble β-hydroxynitriles has not presented problems since classical extraction and chromatographic techniques can be employed. However, such classical extraction techniques are not useful with water-soluble β-hydroxynitriles since they cannot be separated from residual cyanides or cyanide salts, which are also water-soluble.
Product color is another problem encountered during preparation of some water-soluble β-hydroxynitriles, particularly 3-hydroxyvaleronitrile. When β-hydroxynitriles are prepared via a ring-opening reaction from an epoxide and potassium cyanide, a dark-colored refined oil is obtained upon distillation. To be suitable for use, the dark distillate oil must be refined to further reduce impurities, which results in a lighter color or substantially colorless oil. Further refining of dark oil from conventional processes is difficult via conventional distillation techniques.
It would be desirable to have an improved process for preparing β-hydroxynitriles via ring-opening reactions between terminal 1,2-epoxides and inorganic cyanides. It would further be desirable to have a process whereby undesirable by-products are reduced or eliminated. It would further be desirable to have a process that enabled the separation of water-soluble β-hydroxynitriles from cyanide salts and residual cyanides. It would further yet be desirable to have a process for preparing β-hydroxynitriles wherein resulting distillate oils are lighter in color, e.g., a pale yellow color in the instance of 3-hydroxyvaleronitrile. It would further still be desirable to have a process for making β-hydroxynitriles that can easily be adapted to development or commercial scale.